As the need for high performance materials, such as those used in space optics and the aerospace industry continue to expand, it has become increasingly necessary to introduce new technologies to keep up with growing demands. Current technologies try to facilitate the need for reduced area density of space optic materials, while preserving or increasing the stiffness.
Currently, beryllium has been used in space optics applications because it is known as one of the best specific stiffness materials. However, there have been disadvantages associated with the use of beryllium. Beryllium is known to be toxic and carcinogenic, with short to long term exposure, and can lead to health problems. In addition, fabrication of structures with beryllium can be difficult. In particular, beryllium welding without filler material often is limited to thin foils, which can require high-purity, high-performance beryllium components to be machined. For example, creating a high performance mirror from a sandwich panel structure consisting of two face sheets separated by a core can be difficult when starting with solid beryllium.
Recently, there has been interest in using diamond in structures. Diamond is known to have the highest specific stiffness of any material. However, although these diamond structures exist, they are typically random diamond foams. Disadvantages with these random foam structures typically yield mechanical, thermal and electrical properties which are inferior to materials with an ordered, rationally designed and optimized 3-D microstructure.
Silicon carbide random foams have also been used, but can be disadvantageous. Random cell foams typically have lower stiffness-to mass ratios than micro-architected ordered cellular truss materials. Additionally, silicon carbide typically can have a lower stiffness-to-mass ratio than diamond. Furthermore, silicon carbide can also have a higher thermal distortion parameter (ratio of coefficient of thermal expansion to thermal conductivity) than diamond.
Therefore, while these aforementioned diamond structures can be useful, they are often disadvantageously time consuming to make, typically using pyrolysis, sintering, gas-phase or dip coating processes, which can often require additional steps. Furthermore, structures such as foams, are not ordered microstructures, and can suffer from random interconnections in their forms, thereby reducing the strength of the materials per unit weight. In addition, bulk diamond can be expensive and may not be available in large sizes.
The use of three dimensional (3D) ordered polymer cellular micro-truss materials, allows fabrication of optical components with high stiffness-to-mass ratio. Additionally, lower weight is desirable for uses as aerospace components. These 3D ordered polymer cellular structures have been created using optical interference pattern techniques, also called holographic lithography; however, structures made using these techniques have an ordered structure at the nanometer scale and the structures are limited to the possible interference patterns, as described in Campbell et al., “Fabrication Of Photonic Crystals For The Visible Spectrum By Holographic Lithography,” NATURE, Vol. 404, Mar. 2, 2000, which is incorporated by reference herein in its entirety.
Previous works have also been done on creating polymer optical waveguides. A polymer optical waveguide can be formed in certain photopolymers that undergo a refractive index change during the polymerization process. When a monomer that is photo-sensitive is exposed to light (e.g., UV light) under the right conditions, the initial area of polymerization, such as a small circular area, will “trap” the light and guide it to the tip of the polymerized region due to the index of refraction change, further advancing that polymerized region. If the polymer is sufficiently transparent to the wavelength of light used to initiate polymerization, this process will continue, leading to the formation of a waveguide structure, or fiber, with approximately the same cross-sectional dimensions along its entire length. This phenomenon has been suggested for applications, such as fiber optic interconnects, for example. The existing techniques to create polymer optical waveguides have only allowed one or a few waveguides to be formed, and these techniques have not been used to create a self-supporting three-dimensional structure by patterning polymer optical waveguides.
Inorganic polymer materials, such as pre-ceramic polymers have been used to form ceramic micro-truss structures. These pre-ceramic polymers have been used to form specific polymer-based structures that can be subsequently heat treated (pyrolyzed/sintered) to create near net shape ceramic structures.
Advantages of ceramic micro-truss materials include high temperature stability and attractive strength to weight ratios. The importance of these high temperature ceramic micro-truss structures makes these structures amenable to a wide variety of applications, such as the automotive and aerospace industries. These ceramic micro-truss materials could be used for lightweight, high temperature structural applications or for other applications that can utilize the unique porosity, such as thermal ground planes.
Therefore, it is desirable to provide diamond materials with ordered interconnected three-dimensional ceramic microstructures that are lightweight, highly durable, hard materials, and can withstand a high temperature environment. Furthermore, it would be advantageous to use the minimum amount of diamond so that large-scale diamond structures can be fabricated.